1. Field of the Invention
The present invention relates to a tremble preventing device mounted in an optical device, for example, binoculars.
2. Description of the Related Art
Conventionally, an optical device, for example, binoculars, is provided with a tremble preventing device which corrects a tremble of a focused image due to camera-shake and so on. In the tremble preventing device, correction optical systems are moved by a predetermined amount such that a movement of the optical device is canceled, enabling the tremble of the focused image to be corrected. Direct-drivetype actuators that include a stepping motor are utilized as a driving device of the correction optical systems. A rotational motion of the stepping motor is transmitted to the correction optical systems, after being converted to a two-dimensional rectilinear motion of the correction optical systems by a transmitting mechanism, on a plane perpendicular to optical axes of the correction optical systems.
A driving amount of the correction optical systems corresponding to one rotation step of the stepping motor is determined due to an angular degree through which one rotation of the stepping motor moves and a construction of the transmitting mechanism. Accordingly, the driving amount of the correction optical systems can be controlled by a step amount of the stepping motor, so that a position of the correction optical systems can be easily determined.
For example, a gear mechanism or a screw mechanism is utilized as the transmitting mechanism. However, play exists in the engaging portion of such a gear mechanism and a screw mechanism. Thus, when a direction of drive of the engaging portion is reversed, an initial rotational motion of the stepping motor is spent in taking-up the backlash, and is not transmitted to the correction optical systems.
Namely, even if the stepping motor is driven by pulses calculated based on a trembling amount of the focused image, the correction optical systems are not accurately driven due to the aforementioned backlash. In order to prevent the inaccurate driving due to the backlash, a spring member may be mounted, urging the engaging portion in a predetermined direction such that a positional engagement remains unchanged at all times when the driving operation starts.
However, the mounting of the spring member causes an increase in a number of members in the optical device, a rise in a manufacturing cost, and an enlargement in an overall size and weight of the optical device.